The present invention relates to a system for retrieving data, and more particularly to equalizer-target filter pairs designed to retrieve data from bit-patterned magnetic media.
Magnetic media refers generally to disc drives that include one or more discs mounted for rotation on a hub or spindle. The disc drive is typically comprised of a plurality of concentric tracks. Information is stored to the magnetic media by controlling the direction of magnetization, and in particular, to controlling the transition between directions of magnetization along each concentric track. Thus, the transition (or lack thereof) between adjacent areas on the magnetic media defines whether a bit is a ‘1’ or a ‘0’. The storage capacity of magnetic media is increased by continually decreasing the size of individual grains of magnetic material that defines the magnetic media. As the grain size decreases, the density of information that can be stored to the magnetic media increases.
The superparamagnetic limit, however, defines a limit to the size of individual grains, below which the grains become unstable and lose the ability to hold a particular direction of magnetization. A proposed solution to limits imposed by the superparamagnetic limit is the concept of patterned media. As opposed to conventional magnetic media, in which the magnetic media consist of uniform grains, patterned media consists of a plurality of “bit-islands” that each consists of a single grain or several linked grains. Adjacent bit-islands are separated from one another by non-magnetic material. In an effort to further increase density, a concentric track is divided into two or more sub-tracks, with each sub-track staggered in the cross-track direction from adjacent sub-tracks.
The use of patterned media, and in particular to patterned media comprised of sub-tracks, presents additional obstacles related to retrieval of data from the patterned media. For instance, the position of the transducer head relative to each sub-track affects the channel response, and thus, the ability of the system to accurately detect user data. Furthermore, inter-symbol interference (ISI), which refers to a signaling phenomenon in which adjacent symbols blur into one another, increases the complexity associated with decoding user data written to a patterned media.
Equalizers and detectors have been designed to deal with the increasingly complex task of decoding user data. However, most equalizers and detectors are designed for processing data from conventional media, not bit-patterned media. It would be beneficial to improve the design of equalizers and detectors to accommodate differences between conventional media and bit-patterned media.